Conventionally, in tires used in vehicles and the like, improved wet performance (wet grip performance) has been demanded from the perspective of safety while travelling, and reduced rolling resistance has been demanded from the perspective of fuel efficiency. Blending silica in the rubber component constituting the tread portion of a tire is a known method for responding to this problem, but silica has low affinity with rubber components, and the cohesiveness of silica components is high, so even if silica is simply added to the rubber component, the silica is not dispersed, which leads to the problem that the effect of reducing the rolling resistance or the effect of improving the wet performance cannot be sufficiently achieved.
A known method for responding to this problem is blending a mercaptosilane (a silane coupling agent having a mercapto group) capable of reacting with the silica in a rubber composition containing silica, or the like.
As a technique to improve silica dispersibility and wear resistance, the present inventors have proposed the use of a silane coupling agent having a mercapto group or sulfide group and a thiuram disulfide vulcanization accelerator in a rubber composition containing silica (Japanese Unexamined Patent Application Publication No. 2011-190450A).
With conventional rubber compositions containing mercaptosilanes, however, crosslinking (rubber scorch) and the like sometimes occurred at the storage stage or at a stage prior to the vulcanization process, and there was room for improvement from the perspective of processability of the rubber (for example, improving scorch resistance, and improving the balance of scorch resistance and time until vulcanization is complete (acceleration of vulcanization; similarly hereinafter)).
Additionally, even further improvement in wet performance and low rolling resistance has come to be demanded recently.
Additionally, in rubber compositions containing the thiuram disulfide vulcanization accelerator used in the rubber composition described in Japanese Unexamined Patent Application Publication No. 2011-190450A and a conventional mercaptosilane, such rubber compositions do not satisfy the levels of wet performance and processability required recently, and there is room for improvement of wear resistance.